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Observation of top-quark pair production in association with a photon and measurement of the $t\bar{t}\gamma$ production cross section in pp collisions at $\sqrt{s}=7$ TeV using the ATLAS detector

2015-04-28Journal article Open access
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dc.contributor.authorATLAS collaboration (2881 authors)
dc.contributor.authorAguilar-Saavedra, Juan Antonio
dc.contributor.authorAmor Dos Santos, Susana Patricia
dc.contributor.authorAnjos, Nuno
dc.contributor.authorAraque, Juan Pedro
dc.contributor.authorCantrill, Robert
dc.contributor.authorCarvalho, João
dc.contributor.authorCastro, Nuno Filipe
dc.contributor.authorConde Muiño, Patricia
dc.contributor.authorDa Cunha Sargedas De Sousa, Mario Jose
dc.contributor.authorDo Valle Wemans, André
dc.contributor.authorFiolhais, Miguel
dc.contributor.authorGalhardo, Bruno
dc.contributor.authorGomes, Agostinho
dc.contributor.authorGonçalo, Ricardo
dc.contributor.authorJorge, Pedro
dc.contributor.authorLopes, Lourenco
dc.contributor.authorMachado Miguens, Joana
dc.contributor.authorMaio, Amélia
dc.contributor.authorManeira, José
dc.contributor.authorMarques, Carlos
dc.contributor.authorOnofre, António
dc.contributor.authorPalma, Alberto
dc.contributor.authorPedro, Rute
dc.contributor.authorPina, João Antonio
dc.contributor.authorPinto, Belmiro
dc.contributor.authorSantos, Helena
dc.contributor.authorSaraiva, João
dc.contributor.authorSilva, José
dc.contributor.authorTavares Delgado, Ademar
dc.contributor.authorVeloso, Filipe
dc.contributor.authorWolters, Helmut
dc.date.accessioned2019-02-04T05:56:38Z
dc.date.available2019-02-04T05:56:38Z
dc.date.issued2015-04-28
dc.date.updated2019-02-04T05:56:38Z
dc.description.abstractA search is performed for top-quark pairs ($t\bar{t}$) produced together with a photon ($\gamma$) with transverse energy greater than 20 GeV using a sample of $t\bar{t}$ candidate events in final states with jets, missing transverse momentum, and one isolated electron or muon. The dataset used corresponds to an integrated luminosity of 4.59 $fb^{-1}$ of proton-proton collisions at a center-of-mass energy of 7 TeV recorded by the ATLAS detector at the CERN Large Hadron Collider. In total 140 and 222 $t\bar{t}\gamma$ candidate events are observed in the electron and muon channels, to be compared to the expectation of $79\pm 26$ and $120\pm 39$ non-$t\bar{t}\gamma$ background events respectively. The production of $t\bar{t}\gamma$ events is observed with a significance of 5.3 standard deviations away from the null hypothesis. The $t\bar{t}\gamma$ production cross section times the branching ratio (BR) of the single-lepton decay channel is measured in a fiducial kinematic region within the ATLAS acceptance. The measured value is $\sigma_{t\bar{t}\gamma}^{fid} = 63 \pm 8 (stat.) ^{+17}_{-13} (syst.) \pm 1 (lumi.)$ per lepton flavor, in good agreement with the leading-order theoretical calculation normalized to the next-to-leading-order theoretical prediction of $48\pm 10$ fb.
dc.description.versionPeer Reviewed
dc.identifierPhys.Rev. D91 (2015) 072007; DOI 10.1103/PhysRevD.91.072007
dc.identifier.urihttp://dx.doi.org/10.1103/PhysRevD.91.072007
dc.identifier.urihttp://hdl.handle.net/10400.26/26768
dc.language.isoeng
dc.titleObservation of top-quark pair production in association with a photon and measurement of the $t\bar{t}\gamma$ production cross section in pp collisions at $\sqrt{s}=7$ TeV using the ATLAS detector
dc.typejournal article
dspace.entity.typePublication
rcaap.rightsopenAccesspt
rcaap.typearticle

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